"If It Sounds Too Good To Be True, It Probably Is." Cannot be said enough.
A fun shortcut I use to test if someone who is suspicious or especially approaching me with an offer without prompting is to throw some Naija slang at them (This is the street slang used by virtually all Nigerian scammers and often other scammers from all over, it's also spoken by plenty of non-scammers in Nigeria and elsewhere FWIW).
Wait and see what happens.... a simple "alaye" works well, or, if you're feeling creative, search up some other colourful Naija vocab.
"Alaye" is a short hand for "yo, i'm scamming too so don't waste your time" basically. Usually they'll say some pithy or playful shit back or just block you and save you the nanosecond or two. They really don't like it when you call them a fool, use this information cautiously but strategically if need arises.